This is down to the fact the Linx tablets SOLELY use EFI to boot, and you have no LEGACY option at all. The Linx tablets also have a 32-bit EFI environment - which limits them to a 32-bit Windows environment (Windows 32bit EFI loader will only load 32bit Windows). Unfortunately, the 32bit version of Windows 7 will not boot from EFI and is limited to a Legacy/BIOS boot.

None of the cheap modern tablets are capable of running Windows 7. You'd have to look at more expensive pieces of kit (Surface Pro etc) which use EFI64 and surely that would negate the cost of not updating to 8.1 licenses (at about £500 a device).

You also have the conundrum that almost all the new tablets simply don't have the drivers available for windows 7 - so you'll never be able to use the hardware properly. And the fact that Windows 7 is pretty damned poor on tablets compared to 8.1 and 10.